The polyphenylene ethers and processes for their preparation are well known in the art. They are described in Hay, U.S. Pat. No. 3,306,874 and U.S. Pat. No. 3,306,875 and Blanchard et al, U.S. Pat. No. 3,219,625 and U.S. Pat. No. 3,219,626 all of which are incorporated by reference. Other patents which show the preparation of polyphenylene ethers include Price et al, U.S. Pat. No. 3,382,212; Kobayashi et al, U.S. Pat. No. 3,455,880; Bennett and Cooper, U.S. Pat. No. 3,796,689; Bennett and Katchman, U.S. Pat. No. 3,787,362; Cooper, Pat. No. 3,733,307; Cooper and Bennett, U.S. Pat. No. 3,733,299, all of which are incorporated by reference.
The processes most generally used to produce the polyphenylene ethers involve the self-condensation of a monovalent phenol in the presence of an oxygen-containing gas and a catalyst comprising a metal-amine complex.
These processes are carried out in the presence of an organic solvent and the reaction is usually terminated by removal of the catalyst from the reaction mixture. This has been carried out by extraction with mineral acids such as hydrochloric or sulfuric acid. This gives good copper removal, but has the disadvantage that hydrochloric acid is extremely corrosive to stainless steel, so that process equipment must be made of expensive special alloys. The same is true, to a lesser extent, of aqueous sulfuric acid. Both sulfuric and hydrochloric acid tend to react with PPO in solution, introducing small amounts of sulfur or chlorine into the polymer, with a reduction in stability of the polymer under processing conditions.
Extraction with organic acids such as acetric acid has also been used. This procedure also gives good copper removal and extracts both copper and amine into the aqueous phase. A separate step (neutralization and distillation) is required to recover the amine; this is also true for extraction with mineral acid. A major disadvantage is that the effluent water from the plant contains large amounts of sodium acetate. Because of its chemical oxygen demand, environmental regulations require that this be removed before the water is discharged. This is expensive; the water must be impounded and the sodium acetate destroyed by bacterial action before it can be discharged. Also, extraction with chelating agents such as EDTA, triethylene tetraamine, etc., has been employed for this purpose. This procedure gives good copper removal and leaves the amine in the organic phase, so that it can be recovered simply by distillation with the solvent. The main disadvantage is that the chelating agents wind up in the water and environmental regulations prohibit their discharge. The variation on this procedure, in which the extraction step is eliminated and the polymer precipitated directly after addition of the chelating agent, has the same advantages and disadvantages. It has now been found that aqueous solutions of ammonium salts may be used to extract the copper-amine catalyst from a polyphenylene ether reaction mixture. This procedure gives adequate copper removal and does not cause any environmental problems. Most of the amine component of the catalyst remains in the organic phase and can be recovered by distillation with the solvent.
Accordingly, it is a primary object of this invention to provide an effective process for the removal of the copper-amine catalyst from a polyphenylene ether reaction mixture.